Home Forums Design and Building 2 Stroke Amplifier Design and Building Two-Stroke Silent after hours of use Re: Re: Two-Stroke Silent after hours of use


Confirm that the hum is actually coming for the speaker(s) and not just transformer hum. If you know for sure that the signal from the OT is getting to the speaker (hum from the speakers), then check the input jack and connection to pin 2 of V1 (the shielded cable from the input tip lug to lug 2 on the 12AX7 socket), be sure the the input has not shorted to ground. Confirm that the speaker(s) is wired correctly from the OT through the switch, if you accidentally the two secondary taps from the OT together, it will reduce the output to next to nothing.
This can also happen if the feedback loop is wired incorrectly to the speaker jack.

It’s possible that there is an unintended ground somewhere, or that the output tube socket(s) is not making good connection at one of the lugs. (use the chopstick test to poke around and see if you can find a loose or intermittent connection).

Regarding the tone control squeal: use the chopstick test to see if you can reduce or eliminate the noise by moving the leads around, it could be parasitic oscillation.